1. Field of the Invention
Embodiments of the present invention relate to systems and methods for automatically controlling the heading of a tiltrotor aircraft or helicopter experiencing an excessive lateral force. More particularly, embodiments of the present invention relate to systems and methods for automatically commanding a heading change of a tiltrotor aircraft or helicopter when a lateral swashplate position signal or a lateral acceleration signal exceeds a preset limit.
2. Background Information
Rotorcraft can include, but are not limited to, tiltrotor aircraft, helicopters, or autogyros. Rotorcraft can be manned or unmanned aircraft. Manned rotorcraft can be commanded by a pilot. Unmanned rotorcraft can be commanded by a ground control station (GCS) operator or flight control box (FCB) operator. Rotorcraft can, for example, take off and land vertically, move horizontally, or hover in place. Rotorcraft can also generally move or maintain their position in response to external forces by pitching one or more main rotors.
The control systems for rotorcraft are complex electrical and/or mechanical systems. The control systems respond to the pilot or operator's input, but also must accommodate forces acting upon rotor assemblies that are generally outside the control of the pilot or operator. Mechanical control systems typically include a swashplate arrangement that includes a stationary portion and a rotating portion. Typically, the lower, stationary portion is fixed in position and will not rotate, but has the ability to move up and down and/or tilt in any given direction. This is commonly referred to as the “stationary” or “non-rotating” swashplate. Pilot or operator inputs alter the vertical position of the stationary swashplate through the collective control and the tilt or pitch of the stationary swashplate through the cyclic control. The rotating portion of the swashplate arrangement is free to rotate. Of course, pilot or operator inputs to the non-rotating portion are passed through to the rotating portion of the control systems.
Excessive external lateral force can adversely affect the control system of a rotorcraft. Such an excessive external lateral force can include, but is not limited to, a large cross wind (normal to the aircraft heading) experienced by a rotorcraft during hover or landing. Generally, a pilot or operator will command the control system of the rotorcraft to handle the lateral force or cross wind once it is detected. The control system will then tilt the swashplate to oppose the lateral force.
For a tiltrotor aircraft, there are two methods of controlling the lateral velocity and position of the aircraft while hovering with a cross wind. The first method requires tilting the aircraft downward in the lateral axis toward the cross wind. This method requires no lateral cyclic swashplate input, but rather relies upon controlling the differential collective rotor control to hold the lateral aircraft attitude at the required position to yield the desired lateral force to oppose the cross wind. The second method allows the aircraft to hover with a lateral attitude of zero by using the lateral swashplate control to produce the lateral force to oppose the cross wind, while the differential collective control is used to maintain the aircraft level attitude. The second method provides dynamic and operational advantages, but this type of opposition to the lateral force can present at least two additional problems. First, the lateral force can be so large that it exceeds the physical limitations of the control system and swashplate. Second, so much of the control system or tilt in the swashplate is used to oppose the lateral force that there is not enough control left in the control system to fly or land the rotorcraft.
In view of the foregoing, it can be appreciated that a need exists for systems and methods that can monitor the lateral forces on a rotorcraft and automatically change the heading of the rotorcraft if it experiences an excessive lateral force.